The present invention relates to the technical field pertaining to equal channel angular extrusion (ECAE, see References [1] and [2]), one of a range of severe plastic deformation technologies, and more specifically, to equal channel angular drawing (ECAD, see Reference [3]).
ECAE is a process imparting severe plasticity, due to shear deformation, to a metallic material by extruding the metallic material through a die in which two channels (inlet and outlet) having the same cross-sectional areas intersect with each other at an arbitrary angle. As a result, grain refinement and a reduction of spheroidizing time are achieved, and mechanical properties are improved (see Reference [4]). However, even though ECAE is a good severe plastic deformation technology, a continuous process is not possible because it is an extrusion process. Therefore, there is a limitation in the commercialization of ECAE.
Thereafter, ECAD capable of obtaining a material having similar characteristics to a material processed through ECAE and imparting severe plastic deformation as well as performing a continuous process was introduced. Although ECAD, as in the case of ECAE, uses an apparatus in which two channels having the same cross-sectional areas intersect to each other, ECAD is a method of drawing a workpiece instead of the extrusion thereof, as in ECAE. Therefore, ECAD was introduced as a processing technology capable of performing a continuous process, as well as imparting severe plastic deformation. However, since a material may not uniformly fill a die channel of the processing apparatus during a drawing process, i.e., a filling of a material is insufficient, there are limitations in that a cross section of the material is non-uniformly distributed in a length direction after the processing of the material, and necking is generated during the drawing of the material (see Reference [5]).
Although various apparatuses and methods capable of applying severe plastic deformation technology as well as performing a continuous process may be introduced in addition to the foregoing technology (see Reference [6]), materials having severe plastic deformation applied thereto are mainly sheets, and the apparatuses and methods do not suggest a concrete method for a material to be passed through an equal channel angle and to guarantee surface quality and cross-sectional uniformity of the sheets after processing.